Condenser construction

ABSTRACT

The invention contemplates a steam-surface condenser construction wherein an assembly of spaced tube sheets, associated tubes and water boxes is axially compliantly supported with respect to the condenser shell, and wherein the said assembly further includes elongate strain-proportioning mechanism extending between the tube sheets and effectively tying the water boxes to each other independently of tube-sheet connection via the tubes. The strain-proportioning mechanism may take the form of plural spaced elongate members which effectively span the assembly, these members being positioned in substantial alignment with the region of water-box connection to the respective tube sheets.

United States Patent 11 1 Lenhardt 51 Jan. 21, 1975 CONDENSERCONSTRUCTION [75] Inventor: Michael J. Lenhardt, Trenton, NJ.

[73] Assignee: De Laval Turbine Inc., Princeton,

[22] Filed: May 23, 1973 [21] Appl. No.: 362,948

[52] US. Cl 165/111, 165/134, 165/158, 60/95 A, 285/137 R [51] Int. Cl.F28b 1/02, F28f 9/02 [58] Field of Search 165/110-114, 165/134, 158,159, 81; 60/95 A; 285/137 R [56] References Cited UNITED STATES PATENTS2,181,704 11/1939 McNeal 165/114 2,196,641 4/1940 Morgan 60/95 A2,496,301 2/1950 Meixl 165/159 X 2,552,416 5/1951 Farbas.... 165/111 X3,139,926 7/1964 Tinber 165/111 Primary Examiner--Albert W. Davis. Jr.Attorney, Agent, or Firm-Sandoe, Hopgood 8L Calimafde [57] ABSTRACT Theinvention contemplates a steam-surface condenser construction wherein anassembly of spaced tube sheets, associated tubes and water boxes isaxially compliantly supported with respect to the condenser shell, andwherein the said assembly further includes -elongatestrain-proportioning mechanism extending between the tube sheets andeffectively tying the water boxes to each other independently oftube-sheet connection via the tubes. The strain-proportioning mechanismmay take the form of plural spaced elongate members which effectivelyspan the assembly. these members being positioned in substantialalignment with the region of water-box connection to the respective tubesheets.

20 Claims, 6 Drawing Figures PATENTED JMIZI IBIS SHEET 10F 2 PATENTEDJAN? 1 7 sum 20F 2 CONDENSER CONSTRUCTION This invention relates to theconstruction of steamsurface condensers, of the type used to condenseturbine-exhaust steam in large steam-electric power plants.

Modern steam'electric power-plant practice has been in the direction ofproducing ever-larger condensers, of operating at ever-higher pressuresof water used to effect condensation, and at ever-higher flow rates.Choice of materials, section thickness and the like are the normal toolsby which the condenser designer approaches the myriad structuralproblems raised by the power-plant trends, but the new materialsintroduce further problems; conventional techniques are not aloneenough, for example, to achieve adequate compensation for differentialthermal growth between shell and tubes and concurrently provide forassumption of the physical loads resulting from integration of hydraulicoperating pressures.

It is, accordingly, an object of the invention to provide an improvedconstruction and approach to the construction of condensers of thecharacter indicated.

Another object is to provide improved compensation for differentialthermal growth between shell and tubes, in such condensers.

A specific object is to provide the foregoing by a technique wherebysafe control and limitation are achieved, for physical hydraulicqeactionloads on tubes, or tube sheets, and on the joints between tubes and thetube sheets; such loads being for example the result of hydraulicthrusts of water heads and nozzles, weight of water heads and of watercontained therein, and externally applied forces, or any combination ofsuch loads and forces.

Another specific object is to achieve the foregoing objects in a mannerto permit safe use of thinner, more flexible tube sheets and thin-walltubes of higher heattransfer efficiency.

A further specific object is to provide a condenser construction of suchsuperior character as to assure virtually absolute and total protectionfrom potential catastrophic failure, in the event of failure of a joint(or joints) between a tube sheet and one (or more) of the peripheraltubes connected thereto.

Another object is to achieve the foregoing objects with a constructionwhich may be adapted, as to retrofit, to existing condenserinstallations, regardless of the source of original manufacture, suchretrofit being a means of immediately and in relatively short timesolving certain problems of existing installations.

It is also an object to eliminate the requirement for independentwater-box support and for control rods on circulating water connections,where such control rods or supports may have been required by reason ofphysical limitations of the condenser.

A still further object is to provide an improved condenser constructionwherein tube sheets and/or shell flanges are inherently bettermaintained in parallel planes, thus facilitating initial tubingassembly, as well as tube replacement operations.

Other objects and various further features of novelty and invention willbe pointed out or will occur to those skilled in the art from a readingof the following specification, in conjunction with the accompanyingdrawings. In said drawings, which show, for illustrative purposes only,preferred forms of the invention:

FIG. 1 is a simplified view in side elevation, of a condenser to whichthe invention is applied;

FIG. 2 is an enlarged view in perspective. to show part of one end ofthe condenser of FIG. I. with the water box removed from such end;

FIG. 3 is an enlarged fragmentary perspective view of the upper leftcorner of the tube sheet visible in FIG. 2, the fragment being taken atthe vertical section 3-3 of FIG. 2, and with the associated tubesremoved but water box in place.

FIG. 4 is a simplified diagram to illustrate basic elements of one formof the invention; and

FIGS. 5 and 6 are diagrams similar to FIG. 4 to illustrate other formsof the invention.

Referring to FIGS. 1 to 4, the invention is shown in application to acondenser for developing return-feed water from exhaust steam, such asthe exhaust of a steam turbine in a power plant. Such exhaust steamenters with downward flow at an inlet 10 to an expansion hood or funnel11 which covers and supplies the basic housing enclosure or shell 12; afeedwater heater-shell duct 13 is shown passing through hood 1]. A setof horizontal condensing tubes is assembled to and extends betweenspaced vertical tube sheets 14-15, the tubes being generally indicatedin FIG. 1 by limiting upper and lower elevations 1616' of the tubecluster. Each outer face of the tube-tube sheet assembly 14-15-16 isclosed by a water box l7-l7' having a port l818 through which coolingwater is supplied (e.g., at 18) and exhausted (e.g., at 18') aftercoursing all the tubes in the cluster 16-l6'. Condensate accumulates inthe shell volume beneath the tube cluster and in collection boxes 19beneath shell 12, for boiler-feed recycled use.

Support for the tube-tube sheet assembly is by way of an axiallycompliant suspension of the tube sheets at each longitudinal end ofshell 12. As shown, each of the shell ends is closed by a panel ordiagragm 20 that is relatively thin and therefore axially compliant. Atubular member or neck 21 is carried at a central opening in panel 20and projects axially outward to a radially outward flange 22, by whichit is removably secured to the periphery of the tube sheet 14; a weld 24(FIG. 3) unites panel 20 to neck 21, and the outer confines of panel 20will be understood to be part of the welded completion of shell 12. Aflange 23 on the water box 17 registers with the peripheral course offlange 22, so that a series of bolts 25 may rigidly unite flanges 22-23to opposite faces of the tube sheet 14.

In accordance with the invention, elongate strainproportioning members,such as tubes or rods 26 are provided to effectively and directlyinterconnect the water boxes 17-17, thus relieving the joints betweentubes and the tube sheets, and also relieving the tube sheetsthemselves, from having to sustain all axially directed forces. Asshown, the neck 21 is sufficiently elongate to include a portion 21'projecting axially inwardly of the panel 20, and strain-proportioningmember connection is made to portion 21', by diametrically slotting eachrod end to define opposed fingers 27 which are securely welded toportion 21'. The neck 21 provides a convenient means wherebylongitudinal strain-proportioning member forces are assuredly alignedwith the peripheral region of water-box connection to the associatedtube sheet 14, particularly since bolts 25 directly connect neck 21 tothe waterbox flange 23. And, of course, it will be understood that thesectional area of and spacing between strainproportioning members 26should be such as not materially to affect steam flow into thecondensing-tube cluster.

The arrangement of FIG. 5 resembles that which has been described forFIGS. 1 to 4, except that strainproportioning members 30, of size andspacing analogous to those described at 26, are employed as directconnections between tube sheets 14 (15). Thus, ends of members 30 areshown reduced and threaded, being drawn tight against a shoulder whensecured by nuts 31; preferably a plate 32 of width to accommodate theperipheral swath of securing means 25 and 31 substantially relieves thestress load on the tube sheet 14 and enhances the effectiveness ofdirect connection to the water box 17. In the slight modification ofFIG. 6, the water box 33 and its flange 34 are of slightly alteredradial proportions, so that direct strain-proportioning memberconnection to the water-box flange is assured, thus dispensing with anyneed for a stress-relieving plate 32. It will be understood that, ifdesired, as in a retrofit application of the invention to an existingcondenser installation, strain-proportioning members 30 or 26 may beinitially formed at partial or fractional length.

To provide some illustration of the significant effectiveness of theinvention, consider a condenser construction wherein tubes 16 are 44 ft.long, having a capacity of 145,000 sq. ft., i.e., wherein this is thetotal outside surface area of all of the tubes 16. The tube sheets 14-15are 8 ft. wide, 12 ft. high, and 1 inch thick; in view of the nature oftube sheets to flex, it will be assumed that 780 l-inch diameter tubes,taken from the outer three peripheral rows of a normal construction(i.e., without the strain-proportioning members 26, 30, 30') of theinvention, participate in sharing the annularly distributed axial loaddue to hydraulic thrust from the water boxes. Various comparative valuesare tabulated below for such a condenser, for the three conditions of(a) past practice, without strainproportioning members, (b)strain-proportioning member practice with aluminum-brass tubes, and (c)strainproportioning member practice using titanium tubes, all taken foran assumed water-box pressure of 45 psi, meaning a 533,000-lb. axialload to be sustained between tube sheets l4-l5 due to water pressurealone. Strain-proportioning members 26 are assumed to be of low-alloysteel, providing a total effective sectional area of 27 sq. in.,distributed over 12 suitably spaced strain-proportioning members 26.

Generally speaking, from the safety viewpoint it is not desirable topermit the operating dynamic axial load per tube to exceed thirtypercent of the theoretical strength of a tube-tube sheet joint. For thejoint of an aluminium-brass tube to a l-inch thick muntz-metal tubesheet, this strength, the pull-out strength, is conservativelyapproximated at 2,000 lbs.; the aboveindicated maximum axial-loadconditions for such tubes, protected by the invention, are less than 20percent of 2,000 lbs. and are thus well within the desired safety designlimit. Additionally, field hydrostatic prcssures at 150 percent ofdesign capacity can be safely sustained. For the joint of a titanium orstainless-steel tube to a similar muntz-metal tube sheet, this strengthis about 1,300 lbs.; and again, it is seen that the abovenoted maximumaxial-load conditions for such tubes, when protected by the invention,are safely held within the thirty percent level for hydraulic-thrustloads, and to approximately the 10 percent level for the thermalcondition which might result from loss of coolant water.

factor which can be designed into a given installation or which can beprovided as the up-grading retrofit of an existing installation. Notonly is safety realized by reducing the danger of tube-tube sheetpull-out, but the invention also makes it possible to avoid orsubstantially reduce the large force differentials which can severelywarp the tube sheet, with resultant damage to local effectiveness oftube-tube sheet joints, particularly in the peripheral region of thetube bundle. Additionally, any tendency for cooling water to leak viaone or more of the tube-tube sheet joints is materially reduced.

Although shown and described for preferred forms and an illustrativeexample, the invention is not to be considered thus limited. Forexample, in certain existing condensers of the above-indicatedproportions, the tube population in the peripheral region of the tubebundle may be substantially less, for example, 30 percent less, thanindicated, in which case employment of the same number and size ofstrain-proportioning members 26 will still hold the aluminum-brass tubesituation within tolerable safety limits; however, for the titanium-tubesituation, it may be necessary, still within the teachings of theinvention, to augment from 12 to 16, the number of strain-proportioningmembers to safely cover the hydraulic-thrust load condition.

It will be appreciated that bolted connections at 25 Invention, withmembers 26 Conventional AL-Brass Tubes Titanium Tubes (without members26) (t8 BWG) (23 BWG) A. Due to hydraulic thrusts, normal flows: Axialload/tube 672 lbs. 380 lbs. 290 lbs. Tube stress:

Al.-Brass Tubes 4,600 psi 3,200 psi Titanium Tubes 8,800 psi 4,600 psiStrain-member stress 6,000 psi 9,400 psi B. Due to thermal excursion,assuming the extreme case of loss of coolant water: Total strain (e),in./inv 6.15 X 10" 2.85 X l0" Tube strain (m). in./in. 1.85 X 10 1.34 X10" Strain-member strain (e inJin. 4.30 X 10" l.5l X 10' Tube stress.psi 2,900 (compression) 2,000 (tension) Strain-member stress, psi 12,900(tension) 4,500 (compression) Axial load/tube* 370 lbs. lbs.

' 1e. reflecting difference between combined load in peripheral tubes.as opposed to combined axial load sustained by strain members.

(31) are purely illustrative of fastening the various members together.And in other situations, other fastening techniques may be employed,wherein the strain-proportioning members serve at least an equallybeneficial function. For example, should the neck, and adjacenttube-sheet and water-box parts be strengthwelded about theirperipheries, the tube sheet will be deriving less radial-plane supportat its location of fastening to the adjacent water-box and neck regions,so that the strain-proportioning function of members 26 will provide aneven more important contribution to the maintenance of a flat tube sheetwhich will not be likely to degrade the nearby tube-tube sheet joints,under the most adverse conditions.

What is claimed is:

1. A steam-surface condenser, comprising an elongate shell, an assemblyof two spaced tube sheets and associated tubes, longitudinally spacedmeans supporting spaced parts of said assembly within said shell, one ofsaid supporting means being axially compliant, first and second waterboxes defining chambers over the respective outer faces of said tubesheets and communicating with the respective outer ends of said tubes,said boxes being secured to said tube sheets over a peripherallycontinuous mounting region, and a plurality of spaced elongatedstrain-proportioning members securely interconnecting correspondinglyspaced locations along said mounting regions.

2. A condenser according to claim 1, in which a peripherally continuousneck member is interposed between and connects said compliant supportingmeans to the nearby tube sheet.

3. A condenser according to claim 2, in which the peripheral course ofsaid neck member substantially conforms to and registers with themounting region of said nearby tube sheet.

4. A condenser according to claim 2, in which said strain-proportioningmembers are connected to the axially inner end of said neck member.

5. A condenser according to claim 2, in which the other supporting meansincludes a second peripherally continuous neck member connected to theother tube sheet in substantial registration with the mounting region ofsaid other tube sheet, and in which said strainproportioning membersinterconnect the axially inner ends of said neck members.

6. A condenser according to claim 5, in which said other supportingmeans includes an axially compliant connection between said second neckmember and said shell.

7. A condenser according to claim 2, in which said strain-proportioningmembers are directly connected to said tube sheets within andsubstantially independent of said neck member.

8. A condenser according to claim 2, in which said one supporting meansincludes a flat generally radial annular axially compliant plate havingan inner edge peripherally secured to said neck member at a locationbetween the axial ends of said neck member, said strain-proportioningmembers being connected to the axially inwardly extending portion ofsaid neck memher.

9. A steam-surface condenser, comprising an elongate shell, an assemblyof two spaced tube sheets and associated tubes, said assembly beingaxially compliantly supported within and near the respective ends ofsaid shell, water boxes defining chambers over the respective outerfaces of said tube sheets and communicating with the respective outerends of said tubes, said boxes being secured to said tube sheets over aperipherally continuous mounting region, and a plurality of spacedelongated strain-proportioning members securely interconnectingcorrespondingly spaced locations along said mounting regions.

10. A condenser according to claim 9, in which each axially compliantsupport comprises a flat generally radial annular plate having an inneredge connected to the nearby tube sheet and an outer edge connected tosaid shell.

11. A condenser according to claim l0, in which a peripherallycontinuous neck member is interposed between and axially connects theinner edge of one of said plates to the nearby tube sheet.

12. A condenser according to claim 11, in which said neck membersubstantially conforms to and registers with the mounting region of thenearby tube sheet, and in which said strain-proportioning members areconnected to said neck member.

13. A steam-surface condenser, comprising an elongate shell, an assemblyof two spaced tube sheets and associated tubes, longitudinally spacedmeans supporting spaced parts of said assembly within said shell, one ofsaid supporting means being axially compliant and comprising an annularplate secured at its outer edge to said shell, a tubular neck having aradially outward flange at its axially outer end and secured to theinner edge of said plate at a location axially offset from said flange,first and second water boxes defining chambers over the respectiveouterfaces of said tube sheets and communicating with the respectiveouter ends of said tubes, said boxes being secured to said tube sheetsover a peripherally continuous mounting region, said neck having aperipheral contour which substantially conforms to the course of saidmounting region and the water box near said neck having a radiallyoutward flange substantially conforming and being secured to said neckflange, and a plurality of spaced elongated strain-proportioning memberssecurely interconnecting spaced locations along the axially inner end ofsaid neck with correspondingly spaced locations along the mountingregion at the opposite axial end of said assembly.

14. In a steam-surface condenser, two spaced apertured tube sheets,plural tubes extending between said sheets and having end support atcorresponding openings of said sheets, first and second radiallyoutwardly flanged water boxes defining chambers over the respectiveouter faces of said tubes, the flanges of said boxes definingcorresponding peripherally continuous mounting regions in axiallyregistry at outer faces of said tube sheets, means including a pluralityof spaced elongated strain-proportioning members securelyinterconnecting said water-box flanges at correspondingly spacedlocations along said mounting regions, a condenser shell surroundingsaid tubes and strain-proportioning members, and peripherally extendingmeans connecting said mounting regions to axially spaced parts of saidshell, at least one of said last-defined means being axially compliant.

15. A condenser according to claim 1, in which said strain-proportioningmembers are bars having ends passing through said tube sheets andsecured directly to said water boxes.

16. A condenser according to claim 1, in which at least one of saidstrain-proportioning members comprises at least two fractional lengths,one of which is connected to the mounting region at one longitudinalend, the other of which is connected to the mounting region at the otherlongitudinal end, and means rigidly coupling the other ends of saidfractional lengths.

17. A condenser according to claim 1, wherein the material and effectivetotal sectional area of said strainproportioning members are selected,in reference to the materials and sizes and peripheral populationdensity of said tubes, such that normal hydraulic load is substantiallyborne by said strain-supportioning members to the substantial relief oftube-tube sheet joints and of the tube sheets themselves for the regionsof peripheral tubes, and such that, in the event of water supply failureduring a capacity steam exposure of said condenser, the thermalexpansion of said strainproportioning members and tubes will so nearlycorrespond that the difference between axial-load forces on peripheraltubes and on said strain-proportioning members will be held withinlimits at least no greater than substantially fifty percent of thetube-tube sheet joint strength.

18. A condenser according to claim 1, wherein the material and effectivetotal sectional area of said strainproportioning members are selected,in reference to the materials and sizes and peripheral populationdensity of said tubes, such that normal hydraulic load is substantiallyborne by said strain-proportioning members to the substantial relief oftube-tube sheet joints and of the tube sheets themselves for the regionsof pcripheral tubes, and such that, in the event of water supply failureduring a capacity steam exposure of said condenser, the thermalexpansion of said strainproportioning members and tubes will so nearlycorrespond that the difference between axial-load forces on peripheraltubes and on said strain-proportioning members will be held withinlimits at least no greater than substantially the level of axially loadper tube achieved by said strainproportioning members for a fullcapacityhydraulic coolant flow from one to the other of said water boxes.

19. A condenser according to claim 18, in which said level of axial loadper tube is at least no greater than substantially 30 percent of thetube-tube sheet joint strength.

20. A condenser according to claim 18, in which said level of axial loadper tube is at least no greater than substantially 20 percent of thetube-tube sheet joint strength.

1. A steam-surface condenser, comprising an elongate shell, an assemblyof two spaced tube sheets and associated tubes, longitudinally spacedmeans supporting spaced parts of said assembly within said shell, one ofsaid supporting means being axially compliant, first and secOnd waterboxes defining chambers over the respective outer faces of said tubesheets and communicating with the respective outer ends of said tubes,said boxes being secured to said tube sheets over a peripherallycontinuous mounting region, and a plurality of spaced elongatedstrain-proportioning members securely interconnecting correspondinglyspaced locations along said mounting regions.
 2. A condenser accordingto claim 1, in which a peripherally continuous neck member is interposedbetween and connects said compliant supporting means to the nearby tubesheet.
 3. A condenser according to claim 2, in which the peripheralcourse of said neck member substantially conforms to and registers withthe mounting region of said nearby tube sheet.
 4. A condenser accordingto claim 2, in which said strain-proportioning members are connected tothe axially inner end of said neck member.
 5. A condenser according toclaim 2, in which the other supporting means includes a secondperipherally continuous neck member connected to the other tube sheet insubstantial registration with the mounting region of said other tubesheet, and in which said strain-proportioning members interconnect theaxially inner ends of said neck members.
 6. A condenser according toclaim 5, in which said other supporting means includes an axiallycompliant connection between said second neck member and said shell. 7.A condenser according to claim 2, in which said strain-proportioningmembers are directly connected to said tube sheets within andsubstantially independent of said neck member.
 8. A condenser accordingto claim 2, in which said one supporting means includes a flat generallyradial annular axially compliant plate having an inner edge peripherallysecured to said neck member at a location between the axial ends of saidneck member, said strain-proportioning members being connected to theaxially inwardly extending portion of said neck member.
 9. Asteam-surface condenser, comprising an elongate shell, an assembly oftwo spaced tube sheets and associated tubes, said assembly being axiallycompliantly supported within and near the respective ends of said shell,water boxes defining chambers over the respective outer faces of saidtube sheets and communicating with the respective outer ends of saidtubes, said boxes being secured to said tube sheets over a peripherallycontinuous mounting region, and a plurality of spaced elongatedstrain-proportioning members securely interconnecting correspondinglyspaced locations along said mounting regions.
 10. A condenser accordingto claim 9, in which each axially compliant support comprises a flatgenerally radial annular plate having an inner edge connected to thenearby tube sheet and an outer edge connected to said shell.
 11. Acondenser according to claim 10, in which a peripherally continuous neckmember is interposed between and axially connects the inner edge of oneof said plates to the nearby tube sheet.
 12. A condenser according toclaim 11, in which said neck member substantially conforms to andregisters with the mounting region of the nearby tube sheet, and inwhich said strain-proportioning members are connected to said neckmember.
 13. A steam-surface condenser, comprising an elongate shell, anassembly of two spaced tube sheets and associated tubes, longitudinallyspaced means supporting spaced parts of said assembly within said shell,one of said supporting means being axially compliant and comprising anannular plate secured at its outer edge to said shell, a tubular neckhaving a radially outward flange at its axially outer end and secured tothe inner edge of said plate at a location axially offset from saidflange, first and second water boxes defining chambers over therespective outerfaces of said tube sheets and communicating with therespective outer ends of said tubes, said boxes being secured to saidtube sheets over a peripherally continuous mounting region, said neckhaving a peripheral contour whiCh substantially conforms to the courseof said mounting region and the water box near said neck having aradially outward flange substantially conforming and being secured tosaid neck flange, and a plurality of spaced elongatedstrain-proportioning members securely interconnecting spaced locationsalong the axially inner end of said neck with correspondingly spacedlocations along the mounting region at the opposite axial end of saidassembly.
 14. In a steam-surface condenser, two spaced apertured tubesheets, plural tubes extending between said sheets and having endsupport at corresponding openings of said sheets, first and secondradially outwardly flanged water boxes defining chambers over therespective outer faces of said tubes, the flanges of said boxes definingcorresponding peripherally continuous mounting regions in axiallyregistry at outer faces of said tube sheets, means including a pluralityof spaced elongated strain-proportioning members securelyinterconnecting said water-box flanges at correspondingly spacedlocations along said mounting regions, a condenser shell surroundingsaid tubes and strain-proportioning members, and peripherally extendingmeans connecting said mounting regions to axially spaced parts of saidshell, at least one of said last-defined means being axially compliant.15. A condenser according to claim 1, in which said strain-proportioningmembers are bars having ends passing through said tube sheets andsecured directly to said water boxes.
 16. A condenser according to claim1, in which at least one of said strain-proportioning members comprisesat least two fractional lengths, one of which is connected to themounting region at one longitudinal end, the other of which is connectedto the mounting region at the other longitudinal end, and means rigidlycoupling the other ends of said fractional lengths.
 17. A condenseraccording to claim 1, wherein the material and effective total sectionalarea of said strain-proportioning members are selected, in reference tothe materials and sizes and peripheral population density of said tubes,such that normal hydraulic load is substantially borne by saidstrain-supportioning members to the substantial relief of tube-tubesheet joints and of the tube sheets themselves for the regions ofperipheral tubes, and such that, in the event of water supply failureduring a capacity steam exposure of said condenser, the thermalexpansion of said strain-proportioning members and tubes will so nearlycorrespond that the difference between axial-load forces on peripheraltubes and on said strain-proportioning members will be held withinlimits at least no greater than substantially fifty percent of thetube-tube sheet joint strength.
 18. A condenser according to claim 1,wherein the material and effective total sectional area of saidstrain-proportioning members are selected, in reference to the materialsand sizes and peripheral population density of said tubes, such thatnormal hydraulic load is substantially borne by saidstrain-proportioning members to the substantial relief of tube-tubesheet joints and of the tube sheets themselves for the regions ofperipheral tubes, and such that, in the event of water supply failureduring a capacity steam exposure of said condenser, the thermalexpansion of said strain-proportioning members and tubes will so nearlycorrespond that the difference between axial-load forces on peripheraltubes and on said strain-proportioning members will be held withinlimits at least no greater than substantially the level of axialy loadper tube achieved by said strain-proportioning members for afull-capacity hydraulic coolant flow from one to the other of said waterboxes.
 19. A condenser according to claim 18, in which said level ofaxial load per tube is at least no greater than substantially 30 percentof the tube-tube sheet joint strength.
 20. A condenser according toclaim 18, in which said level of axial load per tube is at least nogreater than suBstantially 20 percent of the tube-tube sheet jointstrength.